The invention is in the field of electronic reproduction technology and is directed to an engraving element for an electronic engraving machine for engraving printing cylinders, and to an electronic engraving machine having such an engraving element.
DE-C-2508734 already discloses an electronic engraving machine for engraving printing cylinders with an engraving element. The engraving element has an engraving stylus controlled by an engraving control signal as a cutting tool and moves in an axial direction along a rotating printing cylinder. The engraving stylus cuts a sequence of cups arranged in a printing raster into the generated surface cylinder. The engraving control signal is formed by a superimposition of a periodic raster signal for generating the printing raster with image signal values that define the tonal values to be reproduced between xe2x80x9cblackxe2x80x9d and xe2x80x9cwhitexe2x80x9d. Whereas the raster signal effects an oscillating lifting motion of the engraving stylus for engraving the cups arranged in the printing raster, the image signal values determine the cut depths of the engraved cups corresponding to the tonal values to be reproduced.
DE-A-23 36 089 discloses an engraving element that essentially comprises a rotatory system and an electromagnetic drive for the rotatory system. The rotatory system is comprises of a shaft, an armature, a bearing for the shaft, a restoring element and of a damping mechanism. A lever-shaped stylus holder is attached to the shaft, this carrying the engraving stylus. The electromagnetic drive for the rotatory system comprises a stationary electromagnet charged with the engraving control signal in whose air gap the armature of the rotatory system moves. The drive effects a rotatory motion of the shaft oscillating by small angles, and the stylus holder together with the engraving stylus implements a corresponding, oscillating lifting motion in the direction of the generated surface of the printing cylinder for engraving the cups.
U.S. Pat. No. 4,450,486 discloses an engraving element having a similar design structure.
Given the engraving elements disclosed by DE-A-23 36 089 and U.S. Pat. No. 4,450,486, the components of the engraving element are arranged such with respect to the printing cylinder to be engraved that the oscillating shaft of the rotatory system is aligned approximately tangentially relative to the printing cylinder, and the lifting motion of the engraving stylus ensues in a plane proceeding diametrically through the printing cylinder.
The position of the shaft of a traditional engraving element with respect to the printing cylinder has the disadvantage that forces arising upon penetration of the engraving stylus into the printing cylinder attack asymmetrically at the stylus holder and the engraving stylus, which can be expressed in an asymmetrical geometry of the engraved cups given inadequate mechanical stiffness. Another disadvantage is that, due to the position of the shaft, a heating of the engraving element can lead to faulty cut depths of the cups and, thus, to undesired changes in tonal value.
It is an object of the invention to design an engraving element for an electronic engraving machine for engraving printing cylinders as well as an electronic engraving machine having an engraving element such that an improved geometry of the engraved cups and, thus, an improved engraving quality are achieved.
According to the invention, an engraving element of an electronic engraving machine is provided for engraving a printing cylinder. A shaft oscillates with small rotational angles around a longitudinal axis. A drive is provided for the shaft. A lever-shaped stylus holder is attached to the shaft and has an engraving stylus as a cutting tool which, for engraving, executes a stroke motion in a direction onto a generated surface of the printing cylinder rotating around a rotational axis. The engraving element is arranged with respect to the printing cylinder rotating around the rotational axis such that the shaft proceeds substantially parallel to the rotational axis of the printing cylinder. A stroke motion of the engraving stylus occurs in a plane oriented perpendicular to the rotational axis of the printing cylinder.